Just do it. I had one back in November and out of the 7 groupmates, only 3 of us spoke. I volunteered to speak because it's these situations that help you to adjust to high pressure situations (if you want to call it that) where your heart is racing and you're trying not to stutter. You sound like your stutter isn't too severe either? Speak to your group about it though if you really don't want to do it, but also your instructor.